Treatment of disorders of the outer retina

ABSTRACT

This invention is directed to the use of glutamate antagonists to treat the disorders of outer retina.

This application claims priority from PCT/US99/24502, filed on Oct. 20,1999, which claims priority from U.S. Serial No. 60/105,712, filed onOct. 27, 1998.

This invention is directed to the use of glutamate antagonists to treatdisorders of the outer retina.

BACKGROUND OF THE INVENTION

The pathogenesis of retinal degenerative diseases such as age-relatedmacular degeneration (ARMD) and retinitis pigmentosa (RP) ismultifaceted and can be triggered by environmental factors in those whoare genetically predisposed. One such environmental factor, lightexposure, has been identified as a contributing factor to theprogression of retinal degenerative disorders such as ARMD (Sur Ophthal,1988, 32. 252-269). Photo-oxidative stress leading to light damage toretinal cells has been shown to be a useful model for studying retinaldegenerative diseases for the following reasons: damage is primarily tothe photoreceptors and retinal pigment epithelium of the outer retina(Invest Ophthal & Vis Sci, 1966, 5, 450-472; Sur Ophthal, 1988, 32,375-413, Invest Ophthal & Vis Sci, 1996, 37, 1236-1249); they share acommon mechanism of cell death, apoptosis (Trans AM Ophthal Soc, 1996,94, 411-430, Res Commun Mol Paihol Pharmacol, 1996, 92, 177-189); lighthas been implicated as an environmental risk factor for progression ofARMD and RP (Arch Ophthal, 1992, 110, 99-104; Invest Ophihal & Vis Sci,1996, 37, 775-782); and therapeutic interventions which inhibitphoto-oxidative injury have also been shown to be effective in animalmodels of heredodegenerative retinal disease (Proc Nat Acad Sci, 1992,89, 11249-11253; Nature, 25 1990, 347, 83-86).

A number of different classes of compounds have been reported tominimize retinal photic injury in various animal models: antioxidants,such as, ascorbate (Invest Ophthal & Vis Sci, 1985, 26, 1589-1598),dimethylthiourea (Invest Ophthal & Vis Sci, 30 1992, 33, 450-472; ArchOphthal, 1990, 108, 1751-1752), α-tocopherol (Nippon Ganka GakkaiZasshi, 1994, 98, 948-954), and β-carotene (Cur Eye Res, 1995, 15,219-232); calcium antagonists, such as, flunarizine, (Exp Eye Res, 1993,56, 71-78, Arch Ophthal, 1992, 109, 554-622); growth factors, such as,basic-fibroblast growth factor, brain derived nerve factor, ciliaryneurotrophic factor, and interleukin-1-β (Proc Nat Acad Sci, 1992, 89,11249-11253); glucocorticoids, such as, methylprednisolone (Graefes ArchClin Exp Ophihal, 1993, 231, 729-736), dexamethasone (Exp Eye Res, 1992,54, 583-594); and iron chelators, such as, desferrioxamine (Cur Eye Res,1991, 2, 133-144).

To date, excitatory amino acid antagonists have not been evaluated inmodels of outer retinal degeneration as several studies havedemonstrated that principally inner retinal cells are sensitive toexcitatory amino acid toxicity, while exposure to excitatory to aminoacids has no effect on outer retina photoreceptors and retinal pigmentepithelial (RPE) cells (Exp Brain Res, 1995, 106, 93-105: Vis Neurosci,1992, 8, 567-573). However, when tested in a model of mechanical stressinduced ischemia reperfusion, inner retina function and RPE functionwere moderately protected by dextromethorphan treatment but nosignificant protective effect was measured for outer retina function(Arch Ophihal, 1993, 111, 384-388). Similarly, MK-801 was found to beminimally effective at 60 days in preventing the spread of laser inducedthermal burns to the retina, but did not significantly preventphotoreceptor loss when evaluated at 3 and 20 days post laser exposure(Invest Ophthal & Vis Sci, 1997, 38, 1380-1389).

A series of N-methyl-D-aspartate (NMDA) antagonists including eliprodil,ifenprodil, CP-101,606, tibalosine, 2309BT, 840S, and related structuralanalogs are effective neuroprotectants that are believed to modulateexcitatory amino acid toxicity by interacting at the polyamine bindingsite of the NMDA receptor (Journal of Pharmacology and ExperimentalTherapeutic, 1990, 253, 475-482, British Journal of Pharmacology, 1995,114, 1359-64, Bioorganic & Medicinal Chemistry Letters, 1993, 13, 91-94,Journal of Medicinal Chemistry, 1995, 38, 313845, Journal of MedicinalChemistry, 1998, 41, 1172-1184, Journal of Medicinal Chemistry, 1991,34, 3085-3090, WO 97/09309 Synthélabo, WO 97/09310 Synthélabo). Morespecifically ifenprodil, eliprodil, and CP-101,606 have recently beenshown to preferentially block to the NR1A/NR2B subtype of the polyaminebinding site of the NMDA receptor (Neuroscience Letters, 1997, 223,133-136, Journal of Pharmacology and Experimental Therapeutic, 1996,279, 515-523). The selective interaction of the compounds with thepolyamine site of the NMDA receptor subunit is believed to beresponsible at least in part for both the neuroprotective activity andthe relatively favorable side effects profile of this class of compoundswhen compared to NMDA antagonists that act at other sites on the NMDAreceptor, such as MK-801 and PCP.

In addition to having activity as NMDA antagonists, certain compounds,such as, eliprodil and ifenprodil, have calcium antagonist activity atboth the calcium, N, P, and L channels. (European Journal ofPharmacology, 1996, 299, 103-1 12, European Journal of Pharmacology,1994, 257, 297-301). Other calcium antagonists, such as, flunarizine,have also been shown to be protective in light induced damage models(Exp Eye Res, 1993, 56, 71-78; Arch Ophthal, 109, 1991, 554-62).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the prevention of photic retinopathy by eliprodil and otherglutamate agonists.

FIG. 2 shows protection of the retina from collateral damage due tolaser treatment.

FIG. 3 shows the prevention of collateral retinal laser burn damage byeliprodil and its enantiomers.

The present invention is directed to glutamate antagonists which havebeen discovered to be useful in treating disorders of the outer retina,particularly: age-related macular degeneration; retinitis pigmentosa andother forms of heredodegenerative retinal disease; retinal detachmentand tears; macular pucker; ischemia affecting the outer retina; damageassociated with laser therapy (grid, focal and panretinal) includingphotodynamic therapy (PDT); trauma; surgical (retinal translocation,subretinal surgery or vitrectomy) or light induced iatrogenicretinopathy; and preservation of retinal transplants. As used herein theouter retina includes the RPE, photoreceptors, Muller cells (to theextent they are found in the outer retina), and the outer plexiformlayer. The compounds are formulated for systemic or local oculardelivery.

In our light damage paradigms, antioxidants were either ineffective(alpha-tocopherol) or marginally effective at high doses (ascorbate,vitamin E analogs). Similarly, some calcium antagonists (flunarizine,nicardipine) were moderately effective while others (nifedipine,nimodipine, barnidipine, verapamil, lidoflazine, prenylamine lactate,amiloride) had no effect in preventing light induced functional ormorphological changes. However, it has been discovered that NMDAantagonists are effective in treating disorders of the outer retina.

As used herein the term glutamate antagonist means antagonist of theNMDA receptor channel complex. NMDA receptor antagonists include channelblockers (agents that operate uncompetitively to block the NMDA receptorchannel); receptor antagonists (agents that compete with NMDA orglutamate at the NMDA binding site; agents acting at the glycinecoagonist site or any of several modulation sites (e.g., zinc,magnesiums, redox, or polyamine sites). Disorders of the outer retinaencompasses acute and chronic In environmentally induced (trauma,ischemia, photo-oxidative stress) degenerative conditions of the outerretina (retinal pigment epithelial cells “RPE cells”) in geneticallypredisposed individuals. This would include, but not be limited to,age-related macular degeneration, retinitis pigmentosa and other formsof heredodegenerative retinal disease, retinal detachment, tears,macular pucker, ischemia affecting the outer retina, damage associatedwith laser therapy (grid, focal and panretinal) including photodynarnictherapy (PDT), trauma, surgical (retinal translocation, subretinalsurgery or vitrectomy) or light induced iatrogenic retinopathy andpreservation of retinal transplants. Preferred glutamate antagonistsinhibit excitotoxicity by binding at the polyamine site and have calciumantagonist and/or sodium antagonist, and/or neurotrophic activity. Theglutamate antagonists which have been found to be particularly effectivehave the following structure.

Y,X=OH, H

m=0-3

n, p=1,2

R¹=H, halogen, trifluoromethyl, C1-4 alkyl, OH, C1-4 alkoxy, benzyloxy,C1-16 alkanoyloxy, benzoyloxy or when R²=OH or methoxy in the 4-positionand R³=H then

R¹=hyroxymethyl, carbamoyl, or C1-4 alkoxycarbonyl;

R²=H, halogen, C1-4 alkyl, OH, C1-4 alkoxyl;

R³, R⁴=H, C1-4 alkyl; and

R⁵=H, halogen, trifluoromethyl, C1-4 alkyl, OH, C1-4 alkoxy, benzyloxy,C1-16 alkanoyloxy, benzoyloxy.

These compounds include all isomers and pharmaceutically acceptablesalts.

In the preferred embodiments the glutamate antagonist is2-[4-(4-fluorobenzyl)-piperidino]-1-(4-chlorophenyl)ethanol (eliprodil)and/or its R or S isomers.

Certain compounds of this invention have also been shown to have aneurotrophic effect see U.S. Pat. No. 5,547,963). Since it has beenshown that nerve growvth factor inhibits retinal degeneration in a mousestrain genetically predisposed to retinal degeneration (Graefes ArchClin and Exp Ophthal, 1996, 234 supplement 1, S96-100) the neurotrophicactivity of the compounds of this invention may provide an additionaltherapeutic effect.

In general, for degenerative diseases, the compounds of this inventionare administered orally with daily dosage of these compounds rangingbetween 0.01 and 500 milligrams. The preferred total daily dose rangesbetween 1 and 100 milligrams. Non-oral administration, such as,intravitreal, topical ocular, transdermnal patch, parenteral,intraocular, subconjunctival, or retrobulbar injection, iontophoresis orslow release biodegradable polymers or liposomes may require anadjustment of the total daily dose necessary to provide atherapeutically effective amount of the compound. The compounds can alsobe delivered in ocular irrigating solutions used during surgery see U.S.Pat. No. 5604,244 for irrigating solution formulations. This patent isherein incorporated by reference. Concentrations should range from 0.001μM to 10 μM, preferably 0.01 μm to 5 μM.

The compounds can be incorporated into various types of ophthalmicformulations for topical delivery to the eye. They may be combined withophthalmologically acceptable preservatives, surfactants, viscosityenhancers, penetration enhancers, buffers, sodium chloride, and water toform aqueous, sterile ophthalmic suspensions or solutions. Ophthalmicsolution formulations may be prepared by dissolving the compound in aphysiologically acceptable isotonic aqueous buffer. Further, theophthalmic solution may include an ophthalmologically acceptablesurfactant to assist in dissolving the compound. The ophthalmicsolutions may contain a thickener, such as, hydroxymethylcellulose,hydroxyethylcellulose, hydroxypropylmethylcellulose, methylcellulose,polyvinyl-pyrrolidone, or the like, to improve the retention of theformulation in the conjunctival sac. In order to prepare sterileophthalmic ointment formulations, the active ingredient is combined witha preservative in an appropriate vehicle, such as, mineral oil, liquidlanolin, or white petrolatum. Sterile ophthalmic gel formulations may beprepared by suspending the active ingredient in a hydrophilic baseprepared from the combination of, for example, carbopol-940, or thelike, according to the published formulations for analogous ophthalmicpreparations; preservatives and tonicity agents can be incorporated.

If dosed topically, the compounds are preferably formulated as topicalophthalmic suspensions or solutions, with a pH of about 4 to 8. Thecompounds will normally be contained in these formulations in an amount0.001% to 5% by weight, but preferably in an amount of 0.01% to 2% byweight. Thus, for topical presentation, 1 to 2 drops of theseformulations would be delivered to the surface of the eye 1 to 4 timesper day according to the routine discretion of a skilled clinician.

The preferred compound, eliprodil (or its R or S isomers), is orallybioavailable, demonstrates a low incidence of adverse effects uponadministration, and effectively crosses the blood-brain barrier (Drugsof the Future, 1994, 19, 905-909) indicating that effectiveconcentrations are expected in the target tissue, the retina. Thecompound is described in U.S. Pat. No. 4,690,931. the contents of whichare incorporated herein by reference.

Eliprodil was evaluated in our light induced damage paradigm, a model ofretinal degenerative diseases such as retinitis pigmentosa andage-related macular degeneration. Unexpectedly eliprodil, an excitatoryamino acid antagonist, demonstrated marked potency and efficacy as acytoprotective agent. Both photoreceptor and RPE cells were completelyprotected from light induced functional changes and morphologic lesions.

EXAMPLE 1 Photo-oxidative Induced Retinopathy

Photic retinopathy results from excessive excitation of the retinalpigment epithelium and neuroretina by absorption of visible or nearultraviolet radiation. Lesion severity is dependent upon wavelength,irradiance, exposure duration, species, ocular pigmentation, and age.Damage may result from peroxidation of cellular membranes, inactivationof mitochondrial enzymes such as cytochrome oxidase, or increasedintracellular calcium. Cellular damage resulting from photo-oxidativestress leads to cell death by apoptosis, (Shahinfar, S., Edward. D. P.and Tso, M. O. (1991), A pathologic study of photoreceptor cell death inretinal photic injury. Current Eye Research, 10:47-59: Abler, A. S.,Chang, C. J., Fu, J. and Tso, M. O. (1994), Photic injury triggersapoptosis of photoreceptor cells. Investigative Ophthalmology & VisualScience, 35(Suppl):1517). Oxidative stress induced apoptosis has beenimplicated as a cause of many ocular pathologies, including, iatrogenicretinopathy, macular degeneration, retinitis pigmentosa and other formsof heredodegenerative disease, ischemic retinopathy, retinal tears,retinal detachment, glaucoma and retinal neovascularization (Chang, C.J., Lai, W. W., Edward, D. P. and Tso, M. O. (1995), Apoptoticphotoreceptor cell death after traumatic retinal detachment in humans,Archives of Ophthalmology, 113:880-886: Portera-Cailliau, C., Sung, C.H., Nathans, J. and Adler, R. (1994), Apoptotic photoreceptor cell deathin mouse models of retinitis pigmentosa, Proceedings of National Academyof Science (U.S.A.), 91:974-978; Buchi, E. R. (1992), Cell death in therat retina after a pressure-induced ischaemia-reperfusion insult: anelectron microscopic study. I. Ganglion cell layer and inner nuclearlayer, Experimental Eye Research, 55:605-613; Quigley, H. A., Nickells.R. W., Kerrigan, L. A., Pease, M. E., Thibault, D. J. and Zack, D. J.(1995), Retinal ganglion cell death in experimental glaucoma and afteraxotomy occurs by apoptosis, Investigative Ophthalmology & VisualScience, 36:774-786). Photic induced retinal damage has been observed inmice (Zigman, S., Groff, J., Yulo, T. and Vaughan, T. (1975), Theresponse of mouse ocular tissues to continuous near-UV light exposure.Investigative Ophthalmology & Visual Science, 14:710-713), rats (Noell,W. K., Walker, V. S., Kang, B. S., and Berman, S. (1966), Retinal damageby light in rats, Investigative Ophthalmology and Visual Science,5:450-473; Kuwabara, T. and Gorn, R. A. (1968), Retinal damage byvisible light: An electron microscopic study, Archives of Ophthalmology,79:69-78; LaVail, M. M. (1976), Survival of some photoreceptor cells inalbino rats following long-term exposure to continuous light,Investigative Ophthalmology & Visual Science, 15:64-70), rabbit(Lawwill, T. (1973), Effects of prolonged exposure of rabbit retina tolow-intensity light, Investigative Ophthalmology & Visual Science,12:45-51), squirrel (Collier, R. J. and Zigman, S. (1989), Comparison ofretinal photochemical lesions after exposure to Near-UV orshort-wavelength visible radiation, In M. M. LaVail, R. E. Anderson, andJ. G. Hollyfield (Eds.), Inherited and Environmentally induced RetinalDegenerations. Alan R. Liss, Inc., New York; Collier, R., W. Waldron andZigman, S. (1989), Temporal sequence of changes to the gray squirrelretina after near-UV exposure, Investigative Ophthalmology & VisualScience, 30:631-637), non-human primates (Tso, M. O. M. (1973), Photicmaculopathy in rhesus monkey. A light and electron microscopic study.Investigative Ophthalmology & Visual Science, 12:17-34; Ham, W. T., Jr.,Ruffolo, J. J., Jr., Mueller, H. A. and Guerry, D., III. (1980), Thenature of retinal radiation damage: dependence on wavelength, powerlevel and exposure time, Vision Research, 20:1105-1111; Sperling, H. G.,Johnson, C. and Harwerth, R. S. (1980), Differential spectral photicdamage to primate cones, Vision Research, 20:1117-1125: Sykes, S. M.,Robison, W. G., Jr., Waxler, M. and Kuwabara, T. (1981), Damage to themonkey retina by broad spectrum fluorescent light, InvestigativeOphthalmology & Visual Science, 20:425-434; Lawwill, T. (1982), Threemajor pathologic processes caused by light in the primate retina: Asearch for mechanisms, Transactions of the American OphthalmologySociety, 80:517-577), and man (Marshall, J. Hamilton, A. M. and Bird, A.C. (1975), Histopathology of ruby and argon laser lesions in monkey andhuman retina, British Journal of Ophthalmology, 59:610-630; Green, W. R.and Robertson, D. M. (1991), Pathologic findings of photic retinopathyin the human eye. American Journal of Ophthalmology, 112:520-27). Inman, chronic exposure to environmental radiation has also beenimplicated as a risk factor for age-related macular degeneration (Young,R. W. (1988), Solar radiation and age-related macular degeneration,Survey of Ophthalmology, 32:252-269; Taylor, H. R., West, S., Munoz, B.,Rosenthal, F. S., Bressler. S. B. and Bressler, N. M. (1992), Thelong-term effects of visible light on the eye, Archives ofOphthalmology, 110:99-104; Cruickshanks, K. J., Klein, R. and Klein, E.K. (1993), Sunlight and age-related macular degeneration. The Beaver DamEye Study, Archives of Ophthalmology, 111:514-518).

To determine if eliprodil and other glutamate antagonists can rescueretinal cells from photo-oxidative insult, male Sprague Dawley rats wererandomly assigned to drug or vehicle experimental groups. In Experiment1, rats were dosed with various glutamate antagonists, including:MK-801; eliprodil; and memantine and in Experiment 2, the potency ofeliprodil was compared to the potency of its isomers. In bothexperiments, rats received three intra peritoneal (IP) injections ofeither vehicle or drug at 48, 24, and 0 hours prior to a 6-hour lightexposure to spectrally filtered blue light (˜220 fc). Control rats werehoused in their home cage under normal cyclic light exposure. Theelectroretinogram (ERG) is a non-invasive clinical measurement of theelectrical response of the eye to a flash of light. The a-wave andb-wave are two components of the ERG that are diagnostic of retinalfunction. The a-wave reflects outer retina function and is generated byinteractions between photoreceptor and pigment epithelial cells whilethe b-wave reflects inner retina function, particularly Muller cells.The ERG was recorded after a five day recovery period from dark-adaptedanesthetized rats (Ketamine-HCl, 75 mg/Kg; Xylazine, 6 mg/Kg). The eyes'electrical response to a flash of light was elicited by viewing aganzfeld. ERGs to a series of light flashes increasing in intensity weredigitized to analyze temporal characteristics of the waveform andresponse voltage-log intensity (VlogI) relationship.

Results

Effect of blue-light exposure on vehicle dosed rats: Blue-light exposurefor 6 hours resulted in a significant diminution of the ERG responseamplitude (ANOVA, p<0.001; Bonferroni t-test, p<0.05) compared tocontrols when measured after a 5-day recovery period (FIG. 1-A). Maximuma-wave and b-wave amplitudes were reduced more than 70% in vehicle-dosedrats compared to controls. In addition, threshold responses were lowerand evoked at brighter flash intensities.

Experiment 1 Prevention of Photic Retiniopathiy with GlutamateAntagonists

Rats dosed with MK-801, eliprodil or memantine showed dose-dependentprotection of outer and inner retina function against thisphoto-oxidative induced retinopathy

1.) MK-801. MK-801 provided significant protection of outer and innerretina function against light induced retinal degeneration in rats dosedwith 20 mg/kg. Further, response amplitudes, waveforms, and thresholdresponses were not significantly different than control. Maximum a-waveresponse amplitudes averaged 734.05 μV (SEM=36.79 μV) from controls and537.93 μV (SEM=34.42 μV) from 20 mg/kg dosed rats (See FIG. 1-A).Similarly, maximum b-wave response amplitudes were not significantlydifferent and averaged 1807 μV (SEM=74.32 μV) from controls and 1449.77μV (SEM=68.12 μV) from MK-801 dosed rats. No significant protection ofretinal function was measured in rats dosed with MK-801 at doses of 2 or10 mg/kg.

2.) Eliprodil. Significant preservation of retinal function was alsomeasured in cliprodil (racemic mixture) dosed rats (20 mg/kg) comparedto vehicles (FIG. 1-A). The ERG a- and b-wave were 57% and 53% of normaland 2.4 and 2.2 fold higher than vehicle dosed rats, respectively. ERGsrecorded from rats dosed with eliprodil (2 or 10 mg/kg) were notsignificantly different than vehicles and approximately 32% of normal.

3.) Memantine. As shown in FIG. 1-A, no significant protection of outerand inner retina function was measured in memantine (2 mg/kg) dosedrats. Memantine provided significant protection of outer and innerretina function against light induced retinal degeneration in rats dosedwith 20 mg/kg compared to vehicle dosed rats. However, ERG responseswere significantly lower than normal in rats dosed with 20 mg/kg.

Experiment 2: Comparison of Eliprodil with the R and S Isomer

1.) Eliprodil. Eliprodil (racemic) provided significant protection ofouter and inner retina function against light induced retinaldegeneration in rats dosed with 20 and 40 mg/kg (FIG. 1-B). Maximuma-wave response amplitudes in eliprodil dosed rats with 20 and 40 mg/kgwere 2.4 and 2.25 fold higher, respectively, than vehicle dosed rats.After a 5-day recovery period, maximum a-wave response amplitudesaveraged 395.82 μV (SEM=46.4 μV) from 20 mg/kg dosed rats and 419.85 μV(SEM=63.88 μV) from 40 mg/kg dosed rats. No significant difference inretinal function was detected between either dose group and theseamplitudes were approximately 60% of normal.

2.) R-eliprodil. As seen in FIG. 1-B, R-eliprodil was two-fold lesspotent than eliprodil (racemic). No significant protection of outer an dinner retina function was measured after a 5-day recovery period in ratsdosed with R-eliprodil at 20 mg/kg. Maximum a- and b-wave responses were38% and 36% of normal, respectively. However, R-eliprodil did providesignificant protection of outer and inner retina function against lightinduced retinal degeneration in rats dosed with 40 mg/kg (FIG. 1-B).Response amplitudes were about 2 fold higher than vehicle dosed rats and50% of normal. Maximum a- and b-wave response amplitudes averaged 397.25μV (SEM=77.14 μV) and 812.87 μV (SEM=160.13 μV), respectively. Nosignificant retinal protection was measured in rats dosed with thehighest dose of R-eliprodil. 80 mg/kg. Maximum a- and b-wave responseswere approximately 40% of normal.

3.) S-eliprodil. No significant difference in ERG response amplitude wasmeasured between S-eliprodil (5 mg/kg) dosed rats compared to vehicledosed rats. However, as seen in FIG. 1-B, S-eliprodil was two-fold morepotent than eliprodil (racemic). Significant protection of outer andinner retina function was measured after a 5-day recovery period in ratsdosed with S-eliprodil as low as 10 mg/kg compared to vehicles. Maximuma- and b-wave responses were 64% and 76% of normal, respectively.Significant protection of outer and inner retina function against lightinduced retinal degeneration compared to vehicle dosed rats was alsomeasured in rats dosed with 20 mg/kg. Response amplitudes were about 2fold higher than vehicle dosed rats and approximately 62% of normalafter a 5-day recovery period. Maximum a- and b-wave response amplitudesaveraged 418.04 μV (SEM=56.18 μV) and 1015.95 μV (SEM=141.49 μV),respectively.

SUMMARY

All glutamate antagonists evaluated from this series of compoundsprovided significant rescue of RPE and photoreceptor cells in thisphotic induced retinopathy model. Complete protection was measured inMK-801 dosed rats. The S-enantiomer was the most potent retinoprotectiveagent in this series of glutamate antagonists.

EXAMPLE 2 Retinal Laser Burn Spread Damage

The eye is exposed to high-energy laser radiation during the performanceof retinal photocoagulation therapy (grid, focal and panretinal) orduring photodynamic therapy. This type of therapy is often employedduring treatment of choroidal neovascularization, proliferative stagesof diabetic retinopathy, retinopathy of prematurity, or to repairretinal holes or detachrnents. Associated with this laser therapy istissue destruction leading to vision deterioration. The MacularPhotocoagulation Study found that 20% of the eyes treated for subfovealmacular choroidal neovascularizations (CNV) and 18% of the eyes treatedfor juxtafoveal CNV suffered severe visual loss of six or more lines asa direct result of laser treatment. It is believed that this vision lossresults directly from the expansion of the laser-induced lesion tosurrounding normal neurosensory retina and RPE. Singlet oxygen and otherreactive oxygen species as well as cytokines are generated in the areaof the laser burn and thought to migrate laterally to cause collateralretinal damage. Retinal morphology changes in this area are similar tochanges in our photo-oxidative retinopathy paradigm.

The objective of this study was to quantitate change in laser burn sizein vehicle dosed or eliprodil dosed rats to determine if therapeuticagents could minimize laser burn spread damage. Pigmented Long Evansrats were randomly assigned to control, vehicle or drug dosed groups.Rats were pre dosed (IP) 64, 48, 24, and 2 hours before lasering and 3,19 and 25 hours after receiving 2 to 4 laser burns from an argon laser(spot size 200-microns, power intensity=100 mW, and exposureduration=0.1 seconds). After a 48-hour recovery period, eyes were fixed,dehydrated, and embedded in plastic resin. Histological assessment oflaser burns was performed by flatmounting the retina and sectioning thetissue in a plane tangential to the nerve fiber layer. Using thistechnique, the lesion area in the outer nuclear layer could becalculated using an image analysis system.

Results

Histological assessment of retinal burns 48 hours after laser exposureshowed that lesions were normally confined to the choriocapillaris,retinal pigment epithelium and outer retina. The laser bum center wasmarked by; complete closure of all capillaries, arterioles and venuoles;perforation of Bruch's membrane; pyknosis and necrosis of allphotoreceptor nuclei; and destruction of inner and outer segments.Spread of the lesion into peripheral retina consisted of shortening ofouter segments, inner segment swelling, clumping of melanin granules inthe RPE and choroid, and vacuolization of the RPE. In control andvehicle-dosed eyes, laser burn areas averaged 50,627.07 and 55,243.65μ², respectively (FIGS. 2, 3).

1.) Eliprodil. Treatment with eliprodil (racemic) significantly reducedthe retinal burn area approximately 60% (FIGS. 2, 3) compared tovehicle. The average burn area in eliprodil dosed rats was 22,406 μ²(SEM=3559.3 μ²) No reduction in laser lesion bum size was measured inrats dosed with 10 mg/kg. Laser burn lesion areas averaged 55,411.67 μ²(SEM=2555.47 μ²) in this group of rats.

2.) R-eliprodil. Dosing with R-eliprodil (40 mg/kg) resulted in lesionareas that were 28% smaller than lesions in vehicle dosed rats. Laserburn lesion areas in R-eliprodil dosed rats averaged 36,016 μ²(SEM=4779.49 μ²) and were significantly diflerent than vehicle dosed ornon-injected lesions (FIG. 3). Dosing with R-eliprodil (20 mg/kg)resulted in laser lesion areas that were 16% smaller than lesionsmeasured in vehicle dosed rats but were not significantly different.

3.) S-eliprodil. Laser burn lesion areas in S-eliprodil (20 mg/kg) dosedrats averaged 43,098.5 μ² (SEM=2992.94 μ²). Lesion area was 15% smallerthan lesion areas in vehicle dosed rats but were not significantlydifferent than vehicle controls (FIG. 3).

SUMMARY

Both the R-isomer and the racemic mixture of eliprodil providedsignificant reduction of collateral retinal damage around the laserburn. Eliprodil (racemic) was found to be two fold more potent and twiceas efficacious in this laser burn spread model compared to R-eliprodil.Both of these molecules have nanomolar binding affinities to the NMDAreceptor, compared to S-eliprodil, which was devoid of significantefficacy in this model and has millimolar affinity to the NMDA receptor.

The following formulations are representative and not limiting.

EXAMPLE 3

1.0% Eliprodil Suspension w/v % Eliprodil 1% Hydroxypropylmethylcellulose 0.5% Dibasic sodium phosphate (anhydrous) 0.2% Sodiumchloride 0.75% Disodium EDTA (edetate disodium) 0.01% Polysorbate 800.05% Benzalkonium chloride solution 0.01% + 5% xs Sodium hydroxideadjust to pH 5 Hydrochloric acid adjust to pH 5 Water for injection q.s.to 100% Target Tonicity = 290 mOsm/Kg Target pH = 5

EXAMPLE 4

3.0% Eliprodil Suspension w/v % Eliprodil 3.3% Sodium chloride 0.9%Polysorbate 80 0.1% Water for injection q.s. to 100%

EXAMPLE 5

10 mM IV Solution w/v % Glutamate antagonist 0.384% L-Tartaric acid2.31% Sodium hydroxide pH 3.8 Hydrochloric acid pH 3.8 Purified waterq.s. 100%

EXAMPLE 6

0.3% Solution w/v % Glutamate antagonist 0.33% Sodium acetate 0.07%Mannitol 4.3% Disodium EDTA (edetate disodium) 0.1% Benzalkoniumchloride solution 0.01% Sodium hydroxide pH 4.0 Hydrochloric acid pH 4.0Purified water q.s. 100%

EXAMPLE 7

R-Eliprodil 5 mg Capsules mg/capsule Ingredient (Total Wt. 221 mg) % w/wR-Eliprodil hydrochloride 5.53¹ 2.5% Lactose 206.67 93.52% Sodium starchglycolate 6.6 2.98% Magnesium stearate 2.2 1.00% ¹Equivalent to 5 mgEliprodil as free base.

EXAMPLE 8

S-Eliprodil 50 mg Capsules mg/capsule Ingredient (Total Wt. 221 mg) %w/w S-Eliprodil hydrochloride 55.25¹ 25% Lactose (monohydrate) 156.9571.02% Sodium starch glycolate 6.6  2.98% Magnesium stearate 2.2  1.00%¹Equivalent to 50 mg Eliprodil as free base.

EXAMPLE 9

R-Eliprodil 10 mg Capsules mg/capsule Ingredient (Total Wt. 221 mg) %w/w R-Eliprodil hydrochloride 11.05¹  5% Lactose (monohydrate) 201.1591.02% Sodium starch glycolate 6.6  2.98% Magnesium stearate 2.2  1.00%¹Equivalent to 10 mg Eliprodil as free base.

EXAMPLE 10

Eliprodil 20 mg Capsules mg/capsule Ingredient (Total Wt. 221 mg) % w/wEliprodil hydrochloride 22.1¹ 10% Lactose 190.1 86.02% Sodium starchglycolate 6.6  2.98% Magnesium stearate 2.2  1.00% ¹Equivalent to 20 mgEliprodil as free base.

We claim:
 1. A method for treating disorders of the outer retina whichcomprises administering a pharmaceutically effective amount of aglutamate antagonist.
 2. The method of claim 1 wherein the glutamateantagonist is a polyamine site antagonist.
 3. The method of claim 1wherein the glutamate antagonist is a compound of the formula:

Y,X=OH, H m=0-3 n,p=1,2 R¹=H, halogen, trifluoromethyl, C1-4 alkyl, OH,C1-4 alkoxy, benzyloxy, C1-16 alkanoyloxy, benzoyloxy or when R²=OH ormethoxy in the 4-positionl and R³=H then R¹=hyroxymethyl, carbamoyl, orC1-4 alkoxycarbonyl; R²=H, halogen, C1-4 alkyl, OH, C1-4 alkoxyl; R³,R⁴=H, C1-4 alkyl; and R⁵=H, halogen, trifluoromethyl, C1-4 alkyl, OH,C1-4 alkoxy, benzyloxy, C1-16 alkanoyloxy, benzoyloxy, in apharmaceutically acceptable carrier.
 4. The method of claim 3 whereinthe compound is eliprodil.
 5. The method of claim 4 wherein the compoundis R or S eliprodil.
 6. The method of claim 1 wherein the disorder isselected from the group consisting of: age-related macular degeneration;retinitis pigmentosa and other forms of heredodegenerative retinaldisease; retinal detachment and tears; macular pucker; ischemiaaffecting the outer retina; damage associated with laser therapy (grid,focal and panretinal) including photodynamic therapy (PDT); trauma;surgical (retinal translocation, subretinal surgery or vitrectomy) orlight induced iatrogenic retinopathy; and preservation of retinaltransplants.
 7. The method of claim 6 wherein the compound is eliprodilor its R or S isomer.